As illustrated in FIG. 5, a device of this type, as is known in the art, is so constructed that one endless belt 1 of a pair of crossed endless belts 1, 2, wherein a yarn y is sandwiched, is installed between pulleys 1a, 1b, that are positioned a specified distance apart, and the other endless belt 2 is likewise installed between pulleys 2a, 2b that are positioned a specified distance apart. One pulley 1a with which the endless belt 1 is engaged is connected to an output shaft 3a of a motor 3.
Furthermore, a toothed pulley 4 is connected to the said output shaft 3a. The other pulley 2a with which the endless belt 2 is engaged is connected to a shaft 5, and a toothed pulley 6 is also connected to the said shaft 5. To the toothed pulley 4 that is connected to the said toothed pulley 6 and the output shaft 3a of the motor 3, an endless timing belt 9, which is guided by idlers 7, 8, is installed. The thus constructed device works as follows; starting the motor 3 rotates the pulley 1a that is connected to the output shaft 3a of the motor 3 thereby the endless belt 1 that is installed between the pulleys 1a, 1b and the endless belt 2 that is installed between the pulleys 2a, 2b run through the toothed pulley 4, the endless timing belt 9 and the toothed pulley 6.
Additionally, the conventional yarn false twisting device is so constructed that, after the yarn y is sandwiched between the aforesaid pair of the endless belts 1, 2 and provided with false twist, its tension is detected by a tension detecting element t. When the tension of the yarn y is larger than a predetermined setting or range, a control unit c increases the rotation rate of the motor 3 in order to increase the travelling speeds of the endless belts 1, 2, thereby increasing the feed rate of the yarn y and decreasing the tension of the yarn y.
Similarly, when the tension of the yarn y is smaller than a predetermined setting or range, the control unit c decreases the rate of rotation of the motor 3 in order to decrease the travelling speeds of the endless belts 1, 2, thereby decreasing the feed rate of the yarn y and increasing the tension of the yarn y.
As the conventional yarn false twisting device described above is designed to run one of the pair of the endless belts 1, 2 by using such mediums as the toothed pulley 4, the endless timing belt 9 and the toothed pulley 6, it has a problem in that the power transmission mechanism from the motor 3 is complex, thereby causing the yarn false twisting device itself to become larger and the frequency of servicing to increase.
Furthermore, due to the above construction, it is difficult to change the cross angles of the endless belts 1, 2 by changing the angle of the output shaft 3a of the motor 3 and the shaft 5 of the pulley 2a, over which the endless belt 2 is installed.
The object of the present invention is to solve the above problems of the conventional yarn false twisting device, and to provide a yarn false twisting device with improved travelling speed controlling means of the endless belts in response to changes in yarn tension.